1. Field of the Invention
The present invention relates to a scroll-type fluid transferring machine. More particularly, it relates to a fine adjustment structure of a gap in a scroll type fluid transferring machine used for a compressing machine such as an air compressor or a refrigerant compressor, a pump, an expansion machine and so on.
2. Description of Prior Art
The principle of the scroll-type fluid transferring machine has been known long ago and application of the machine to various apparatuses such as compressors, pumps, expansion machines has been studied.
FIG. 29 are diagrams showing a basic construction of a scroll-type fluid transferring machine. In FIG. 29, a reference numeral 1 designates a stationary scroll member, a numeral 2 an oscillatable scroll member, a numeral 1a an outlet port, a symbol P a compression chamber, a symbol O the center of the stationary scroll member, a symbol O' the center of the oscillatable scroll member 2. The stationary and oscillatable scroll members 1, 2 respectively have a spiral wrap plate 101 or 201 on each base plate in one piece. The wrap plates 101, 201 have the same shape but has the inverse direction of winding. The wrap plates 101, 201 of the stationary and oscillatable scroll members 1, 2 are combined with each other as shown in FIG. 29 so that the side surfaces of the plates are brought to contact with each other at a point B. The shape of the wrap plates 101, 201 is constituted by an involute curve or the combination of other suitable curves.
The operation of the scroll-type fluid transferring machine when operated as a compressor will be described.
In FIG. 29, the stationary scroll member 1 is kept stationary and the oscillatable scroll member 2 is combined with the stationary scroll member 1 to be subjected to oscillating movement without changing its posture in the space. FIG. 29 shows each state of the stationary and oscillatable scroll members 1, 2 at angle positions of 0.degree., 90.degree., 180.degree. and 270.degree.. As the oscillatable scroll member 2 moves, the point of contact B moves toward the center whereby gas confined in a crescent-shaped compression chamber P formed between the wrap plate 101 of the stationary scroll member and the wrap plate 201 of the oscillatable scroll member is gradually compressed and is finally discharged through the outlet port 1a. In this case, the distance between the centers O and O' is kept constant (FIG. 29). Namely, OO'=Z/2-t wherein the distance between the wrap plates 101, 201 is Z and the thickness of the wrap plates is t. The distance Z corresponds to the pitch between the wrap plates 101, 201. In FIG. 29, when the oscillatable scroll member 2 is oscillated in the reverse direction, the scroll-type fluid transferring machine functions as an expansion machine.
Now, a concrete construction of the scroll-type fluid transferring machine operating according to the above-mentioned principle will be described with reference to FIG. 30. FIG. 30 shows a conventional scroll-type fluid transferring machine applied to a compressor. In FIG. 30, the same reference numerals as in FIG. 29 designate the same or corresponding parts. Reference numerals 102 and 202 respectively designate the base plates of the stationary and oscillatable scroll members 1, 2, symbols A designate gaps in the axial direction formed between the end surface 101a of the wrap plate 101 and the bottom surface 202a of the base plate 202 and between the end surface 201a of the wrap plate 201 and the bottom surface 102a of the base plate 102.
The oscillatable scroll member 2 is combined with the stationary scroll member 1 so that a surface of the base plate 202 which is opposite the surface having the wrap plate 201 is supported by a frame 4. The stationary scroll member 1 is fixed to the frame 4.
When a main shaft 3 is rotated as shown by the arrow mark, the oscillatable scroll member 2 engaged therewith commences its operation. In this case, the oscillatable scroll member 2 is subjected to revolution around its center without rotation around its center by means of a rotation preventing device though it is not shown in the Figure. As a result, a fluid to be compressed is sucked through an intake port 1b and the fluid compressed according to the principle of operation shown in FIG. 29 is discharged through the outlet port 1a.
In the fluid transferring machine, an amount of the fluid leaked through the gaps A in the radial direction of the wrap plates is relatively large in comparison with the volume of the fluid taken in the compression chamber since the length of the portions where leakage occurs corresponds to the length in the longitudinal direction of the wrap plate on the assumption that the wrap plate is developed. Thus, the leakage of the fluid largely influences efficiency of operation of the fluid transferring machine.
As a method of providing sealing in the radial direction of the wrap plate spirally wound, there is considered means to minimize the gaps as disclosed, for instance, in Japanese Unexamined Patent Publication No. 46081/1980. Namely, leakage of the fluid to be compressed is prevented by introducing oil together with the fluid to be compressed through the intake port 1b so that an oil film is formed in the minute gaps A. However, in order to form such minute gaps uniformly, high accuracy in dimensions of the stationary and oscillatable scroll members 1, 2, the frame 4 and other elements is required. There are problems in machining and assembling operations. For instance, in some case, selective fitting of parts is required in the assembling operations.
During the operations of the machine, the outlet port 1a and the neighboring portions are heated by the compressed fluid with the consequence that if there is caused thermal expansion beyond the distance of the minute gaps A at any local portion, there takes place undesired mechanical friction. To avoid such phenomenon, it is necessary to broaden the gaps A taking consideration of the quantity of thermal expansion. However, this does not provide the optimum gaps required to form an effective oil film with the result that leakage of the fluid becomes large to deteriorate the sealing effect.
Besides such a non-contact sealing method, there is another proposal of preventing leakage of the fluid. Namely, a groove is formed in the end surface of the wrap plate 101 or 201 in its longitudinal direction of the wrap, and a sealing material is fitted in the groove thereby providing a contact sealing means. Such a sealing method is formerly disclosed in U.S. Pat. No. 801,182 in 1905, and is recently disclosed in Japanese Unexamined Patent Publication No. 117304/1976.
The sealing means disclosed in Japanese Unexamined Patent Publication No. 117304/1976 will be described as an example with reference to FIGS. 31 to 34.
FIG. 31 is an enlarged cross-sectional view showing a gap A and its neighboring portion formed between the bottom surface 102a of the stationary scroll member 1 and the end surface 201a of the wrap plate 201 of the oscillatable scroll member 2. A groove 5 of a rectangular shape in cross-section is formed in the end surface 201a of the wrap plate 201 so as to open along the longitudinal direction of the wrap plate. A sealing member 51 having the analogous shape to the groove 5 is fitted in the groove 5. Dimensions of the groove 5 and the sealing member 51 are so determined that a first gap 501 is formed between the first side surface 5b of the groove 5 and the first side surface 51b of the sealing member 51 along the longitudinal direction of the wrap plate, and a second gap 502 is formed between the bottom surface 5d of the groove 5 and the lower surface 51d of the sealing member 51. Accordingly, a gas flowing from a high pressure side compression chamber P.sub.H to a low pressure side compression chamber P.sub.L is passed through the first and second gaps 501, 502 as indicated by the solid arrow marks to exert a force in the direction indicated by F. The upper surface 51a of the sealing member is urged to the bottom surface 102 of the base plate and the second side surface 51c of the sealing member 51 is urged to the second side surface 5c of the groove 5 to prevent leakage of the gas, even though there exists the gap A between the end surface 201a of the wrap plate 201 and the bottom surface 102a of the base plate.
Although such sealing method is effective for the leakage of the gas in the direction along the wrap plate, leakage of the gas easily takes place in the longitudinal direction of the wrap plate through the first and second gaps 501, 502 between the high and low compression chambers P.sub.H and P.sub.L which is partitioned at the point of contact B by the wrap plates 101, 201.
The disadvantage of the above-mentioned method will be described in detail with reference to FIGS. 32 and 33. FIG. 32 is a partly cross-sectioned plane view showing the area of the point of contact B between the wrap plates 101, 201, and FIG. 33 is a perspective view partly cross-sectioned.
FIG. 32 shows that the gas leaks to the low pressure side compression chamber P.sub.L at the downstream side of the high pressure side compression chamber P.sub.H through the first and second gaps 501, 502 as shown by the solid arrow marks. In this method, although sealing function in the radial direction of the wrap plate is effective, the leakage of the gas in the longitudinal direction of the wrap plate unavoidably occurs since the first and second gaps 501, 502 are formed between the groove 5 and the sealing member 51; thus, reduction in compression efficiency or performance is unavoidable. Particularly, scattering in dimensions of the first and second gaps 501, 502 possibly increases leakage of the gas passing through the gaps 501, 502 and the leakage of the gas in the radial direction of the wrap plate due to reduction in ability of following-up of the sealing member 51. Further, loss of the sliding movement and wearing of the upper surface 51a of the sealing member 51 are not negligible because the upper surface 51a is pushed at the bottom surface 102a during the sliding movement.
As means for preventing leakage of the gas in the longitudinal direction of the wrap plate, there is a proposal in Japanese Unexamined Utility Model Publication No. 180182/1982. Namely, as shown in FIG. 34, the width D of the sealing member 51 is substantially equal to the width D' of the groove 5, and the thickness H of the sealing member 51 is made greater than the depth H' of the groove 5. However, it is difficult to control the dimensions H and H'. If H-H'&gt;A, the gap in the axial direction of the scroll members becomes large to thereby increase in an amount of the gas leaked in the radial direction of the scroll members. If H-H'&lt;A, the gap A is too small whereby smooth rotation can not be obtained.
Thus, in the conventional scroll-type fluid transferring machine of the non-contact sealing type, if a uniform minute gap is to be formed in the axial direction, there is the problem of controlling accuracy in dimension of the scroll members to be finished. Further, if the gap is to be narrowed, there is the problem that the end surface of the wrap plates come in contact with the bottom surface due to thermal expansion during the operation of the machine to thereby cause frictional heating. If the gap is broaden to prevent the friction, performance of the fluid transferring machine is reduced. Thus, there is contradiction.
In the conventional scroll-type fluid transferring machine of the contact sealing type, there is the problem of reduction in performance caused by the leakage of the gas through the gap and the wearing of the sealing member when the first and second gaps are formed between the sealing member and the groove so that the sealing member is pushed by the pressure of the gas. Further, when the sealing member is used without forming any gap between the sealing member and the groove, severe requirement of accurate dimensions is required as in the non-contact sealing type.